Apparatus for capping wide web reclosable fasteners

ABSTRACT

An apparatus for capping a stem web including a cooled roll, a first heated nip roll positioned to form a first nip with the cooled roll, and a second heated nip roll positioned to form a second nip with the cooled roll. The cooled roll has a diameter that is at least  30 % larger than a diameter of the first or second heated nip roll. In an embodiment, the two nips are on opposite sides of a larger central cooled roll positioned between the heated rolls. In an embodiment, the reaction forces between the rolls are measured and controlled at each end of each of the heated rolls. The invention is particularly adapted to making abrasive particles that are attached to a driving mechanism via headed stem fasteners formed by the method.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 10/002560, filed Nov.1, 2001, now U.S. Pat. No. 6,843,944; the disclosure of which is hereinincorporated by reference.

TECHNICAL FIELD

The present invention is directed to a method and apparatus for cappingheaded stem releasable fastening webs, and more particularly, to amethod and apparatus that can cap the stems when the width of the web isgreat.

BACKGROUND OF THE INVENTION

Releasable mechanical fasteners are widely used for a vast array ofproducts and applications. One class of such fasteners is thehook-and-loop variety, which include one part having multiple hookshaped projections, and another part presenting a large number of looseloops of fabric or fiber intended to snag on the hooks. Such fastenershave found particular success in e.g. garment manufacturing, and arecommercially available under e.g. the Velcro™ brand-name from the VelcroUSA Inc and under the SCOTCHMATE brand-name from Minnesota Mining &Manufacturing Co. of St. Paul. More recently releasable fasteners thatare self-mating, e.g. where both parts of the fastener are identicallyconstructed and mutually interengage, have become available. One suchexample is the Dual Lock™ reclosable fasteners commercially availablefrom Minnesota Mining & Manufacturing Co. of St. Paul, Minn. Both typesof reclosable fasteners can be fabricated by preparing a web havingprojecting stems thereon (herein referred to as “stem web”) and thencapping those stems to form an array of shaped projections. The stemwebs typically have an indefinite length and given width. The capping ofthe stems is done against a heated roll as described in U.S. Pat. No.5,679,302, the entire contents of which are hereby incorporated byreference. A limitation with this process is that the gap between therolls must be precisely controlled in order to maintain the finalthickness of the product and the size of the caps. Another limitation isthat the process is only suitable for relatively lower line speeds.

A more recent development in capping processes for stem webs was theinvention of a continuously tapered nip or capping shoe. Such anapparatus is described in U.S. Pat. No. 6,039,911, the entire disclosureof which is hereby incorporated by reference. The main advantage of thisdesign is that more contact with the heated roll allows the process tobe run at higher line speeds. However, it was found that difficultieswere encountered when extrapolating the method to wider web widths. Themethod involves a variable nip, and the exact dimension of the gap atthat nip is very important. At wider web widths, roll deflection due tomechanical bending or non-uniform temperatures makes it difficult toachieve a gap that has a uniform dimension across the entire roll. Thiscan be partially balanced with larger roll diameters, but that leads toother problems with weight, cost and thermal control.

More recently then, expedients adapted from roll processes used for thecalendering of paper, plastic and magnetic media have been used for themaking of self mating fasteners. These processes stack several rollstogether so that there are loads on both sides of most of the rolls. Inthis process the capping is accomplished in a series of incrementalsteps, which lowers the peak force required in each step and lowers theamount of roll deflection.

FIG. 1 a shows a conventional calendering process for capping stem webs.In FIG. 1 a, the stem web 10, having a backing 12 and stems 14 thereon,is maneuvered over idler 16 and directed into a nip between heated roll20 and cooled roll 24. The stem web 10 is then directed through a secondnip 28 between cooled roll 24 and heated roll 30. The stem web 10 thenpasses through a third nip 32 between heated roll 30 and cooled roll 34,and then a fourth nip 36 between cooled roll 34 and heated roll 38. Thestem when 10 is then directed to a fifth nip 40 between heated roll 38and cooled roll 42. At last, the stem web 10 is directed to a sixth nip44 between cooled roll 42 and heated roll 46. At last, the fully cappedweb 48 is then drawn off. It should be noted that because heated roll 20at the top and heated roll 46 on the bottom are loaded on only one side,they have a larger diameter to minimize deflection. This process hasbeen successfully used to fabricate HookIt II brand abrasive sandingdisks commercially available from Minnesota Mining & Manufacturing Co.of St. Paul, Minn.

Referring now to FIG. 1 b, a detail side view of a portion of fullycapped stem web 48 according to conventional processes requiring threeor more nips to finally cap the stem web. The figure is used to definereference dimensions for capped stem webs. In this view, one stem 14 isseen in isolation, extending from backing 12 and having a diameter “d”.The use of conventional processes, such as that disclosed in FIG. 1 a,has stem 14, forming cap 50, resulting in capped stem 52. The cap 50 hasa diameter “D”. A convenient way of expressing the degree of cappingachieved is the ratio of D:d. For the Hook-it™ II product, a D:d ratioof approximately 1.66 is achieved at the end of the process, and thisratio is found to give the desired strength of the bond with loopmaterial. The method results in capped stems 52 having a goodsymmetrical shape without buckling, and a consistent result across thewidth of the capped web 48 if the web width is less than 1 meter and theline speed is less than about 30 m/minute. However, the complexity ofthis mechanism, and the difficulty of properly gauging six distinct butinteracting nips have proven to have disadvantages. Also, the process isproved to be unwarrantedly difficult when attempting to extrapolate tolarger diameter stems and faster line speeds. But simpler methods haveproved elusive; for example, with the process according to FIG. 1 a, D:dratios of only about 1.44 being achievable at second nip 28. The artstill requires a method for capping stem webs that is simple, usablewith wider web widths, and capable of running at higher web speeds evenwhen processing stem webs with stems of greater diameter.

SUMMARY OF THE INVENTION

The present invention permits stem web to be prepared in greater widthat greater line speed than has previously been possible. It accomplishesthis by recognizing that the problem of introducing enough heat energyto the tops of the stems so that they can be deformed is not always themost vital. As line speeds and stem diameters increase it becomes moreand more difficult to remove enough heat energy from the stems so thatthey will not be deformed on the next capping pass. The methods andembodiments of the present invention emphasize the importance ofsufficient and timely cooling. In one aspect, the invention provides amethod for capping a stem web, a stem web being a material having abacking and a plurality of stems having a diameter “d” extending fromthat backing. The method includes passing the stem web through a firstnip against a first heated nip roll so as to partially cap the stems;cooling the web; and passing the stem web through a second nip against asecond heated nip roll to completely cap the stems to a diameter “D”.The ratio of D:d is at least 1.5:1, and preferably at least 1.65:1. Inpreferred embodiments, during the passing steps the stem web is moved ata line speed of at least 30 m/minute.

In less technical terms, the partially capped stem web is cooled so welland so fast that the stems that were warm and weak after passing throughthe first nip regain their strength before being subjected to a secondnip. With their strength restored, the second nip can finish the job ofcapping which up until the present invention had to be done in multiplepasses for fear of collapsing the stems.

An alternative way of expressing the present invention is that itprovides a method for capping a stem web, said stem web having a backingand a plurality of stems having a diameter “d” extending from thebacking, the method comprising:

passing the stem web through a first nip so as to partially cap thestems;

cooling the stem web; and

passing the stem web through a second nip to completely cap the stems toa diameter “D”, wherein

the ratio of D:d is at least 1.5:1.

Preferably, the cooling step is performed by contacting the stem webagainst a cooled roll, and more preferably the first nip is between afirst heated nip roll and the cooled roll. Also preferably, the secondnip is between a second heated nip roll and the cooled roll.Conveniently, the stem web contacts the cooled roll for at least 20% ofits circumference so that the requisite amount of cooling can beaccomplished. In some preferred embodiments the stem web contacts thecooled roll for at least 25%, or even 30% of its circumference. In orderto accommodate these preferences, it is particularly convenient that thediameter of the cooled roll is at least 30% larger than the diameter ofthe first nip roll, and also that the diameter of the cooled roll is atleast 30% larger than the diameter of the second heated nip roll.

In cases where both nips are against a single cooled roll, it iscurrently considered preferred that the forces between the first heatednip roll and the cooled roll, and the forces between the second heatednip roll and the cooled roll, are measured at both ends of each roll.These measurements are then used to adjust the positions of the rolls.In most circumstances, these adjustments act so as to equalize the fourreaction forces acting between the rolls at the four measurementlocations. This expedient is one of several things that are included inpreferred embodiments so that wide stem webs may be capped with a veryconsistent result across their entire width. In particular, it is highlydesirable that the capping operation is carried out without bending orbuckling the stems. Caps that are symmetrical about the axis of the stemand not bent over relative to the surface of the backing usually providebetter results in most applications where headed stem fasteners arerequired. Processes that would bend the stems during the cappingoperation by more than 4 degrees from perpendicular to the plane of thebacking are less desirable. The method of the present invention canexceed this criterion even when the width of the stem web is over 1meter, and when the line speed is at least 30 m/minute.

In this aspect, the present invention can be considered as an apparatusfor capping a stem web. This apparatus has a cooled roll, a first heatednip roll positioned to form a first nip with the cooled roll, and asecond heated nip roll positioned to form a second nip with the cooledroll. It has sensors for measuring the forces between the first heatednip roll and the cooled roll, and the forces between the second heatednip roll and the cooled roll, at both ends of each roll. It also hasactuators for adjusting the positions of the rolls based on the outputof the sensors.

One application for which the present invention is particularly suitedis the making of self-mating abrasive articles, and such articlesthemselves. In the abrading art, a perennial problem is the attachmentof an abrasive article to some mechanism which provides relative motionagainst a workpiece. Such mechanisms include, e.g. rotary or orbitalsanders. Clamps or adhesives are traditional expedients for releasablyattaching an abrasive article, e.g. sandpaper to the mechanism.Self-mating connection systems have been considered in this context, butthe high shear forces involved in sanding and grinding have heretoforebeen a limitation. But the thick-stemmed stem webs that the presentinvention can consistently cap, even in the widths necessary foreconomical high-volume commercial production of abrasives, defy thislimitation.

Therefore, in another aspect, the present invention provides a methodfor making an abrasive article, the method comprising:

providing stem web comprising a backing having a first and second,opposite major surfaces, and a plurality of stems having a diameter “d”extending from at least a portion of the first major surface of thebacking;

passing the stem web through a first nip against a first heated nip rollso as to partially cap the stems;

cooling the web;

passing the stem web through a second nip against a second heated niproll to completely cap the stems to a diameter “D”, wherein the ratio ofD:d is at least 1.5:1; and

applying an abrasive layer onto at least a portion of the second majorsurface.

In some preferred embodiments, the abrasive layer is applied by applyinga make coat onto at least a portion of the second major surface of thebacking; at least partially embedding abrasive particles in the makecoat; at least partially curing the make coat; applying a size coat overat least a portion of the at least partially cured make coat andabrasive particles; and curing the size coat. The abrasive layer may beapplied onto at least a portion of the second major surface prior topassing the stem web through the second nip, or it may be applied afterpassing the stem web through the second nip.

In analogy with the methods described above, when making the abrasivearticle is presently considered preferred to use two heated rollers eachproviding a capping nip against a larger cooled roll between them. It isconsidered particularly preferred to measure the forces between thefirst heated nip roll and the cooled roll, and the forces between thesecond heated nip roll and the cooled roll, at both ends of each roll,and to use these measurements to adjust the positions of the rolls.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic view of a known process for capping stem webs;

FIG. 1 b is a detail side view of a capped stem according to the knownprocess illustrated in FIG. 1 a;

FIG. 2 is a schematic view of a process according to the presentinvention for capping stem webs; and

FIG. 3 is a side view on a representative abrasive article preparedaccording to the present invention.

DETAILED DESCRIPTION

Referring now to FIG. 2, an exemplary the apparatus 100 according to thepresent invention is illustrated. In this Figure, the stem web 102,having a backing 104 and stems 106 thereon, is maneuvered over idlers108 and into contact with a heated roll 110. The stem web 102 is nippedbetween first heated roll 110 and cooled roll 114. Within this nip 116,the stems 106 are deformed so as to provide partial caps 118. It is tobe noted that after emerging from nip 116, the stem web 102 remains incontact with cooled roll 114 in a region 120 which is preferably atleast 20%, more preferably at least 25%, and even more preferably 30% ofthe circumference of cooled roll 114. It has been observed in thedevelopment of the present invention that under certain conditions therate of cooling becomes a limiting factor. Therefore, in preferredembodiments the cooled roll is deliberately larger than the heated rollsso that it has more thermal mass for the removal of heat from the stemweb 102, and so that a given percent of the circumference is great inabsolute terms as well as relative terms.

After passing to the cooling region 120, the stem web 102 is taken offand reoriented by idlers 122 and 124. The stem web 102 is then nippedbetween the second heated roll 128 and the cooled roll 114. The gap inthis nip 132 is gauged so as to form caps 134 of finished size indiameter. After passing to the nip 132 the capped web 136 is once againcooled against the cooled roll 114 in a region 138. As before, inpreferred embodiments region 138 is preferably at least 20%, and morepreferably at least 25% of the circumference of the cooled roll 114. Ithas been found in connection with the present invention that is possibleto do a significant amount of deformation in only two passes becauseduring the intense cooling performed in region 120 the stems have achance to regain their structural integrity. The capped stems 134 alsoregain strength in region 138 so that the capped stem web 140 can betaken off around idler 142. The rolls 110, 114, and 128 are convenientlyfabricated from materials, such as for example stainless-steel, so as toprovide a substantial thermal mass and minimize temperaturefluctuations. The heated rolls 110 and 128 are conveniently heated byelectrical heaters on their inside surfaces, or the alternative by hotwater or oil circulating through internal passages. The cooled roll ismost conveniently cooled by means of a cold water circulation system inways well understood by the ordinary artisan. One advantage of apparatus100 is that it can utilize rolls 110, 114, and 128 having nominal widthsof 1 meter or greater. Additionally, the wide rolls can be used atprocessing line speeds of greater than 34 m/minute.

Those skilled in the art recognize that the inventive aspect of thepresent method may be practiced utilizing equipment other than rolls toprovide a nip. For example, rotating belts may be incorporated to formthe nip. Additionally, the nip profile may change depending on thematerial of the stem web and the specific cap desired. Those skilled inthe art of stem web capping are capable of providing nip profiles toobtain a desired end product.

The apparatus 100 is suitable for use with different stem web 102 ofdiverse materials and dimensions. Stem web is conveniently made from avariety of materials as described in U.S. Pat. No. 5,679,302, previouslyincorporated by reference. For example, a copolymer of polypropylene andpolyethylene containing 17.5% polyethylene and having a melt index of30, commercially available as SRD7–560 from Union Carbide Co. ofSeadrift, Tex., is considered particularly suitable. The preparation ofstem web suitable as input material for the capping operation can bedone in several ways, one of which is described in U.S. Pat. No.5,679,302 in connection with e.g. FIG. 6A in that document.

The present invention cools the heated stem web to a point where thematerial regains some of its original strength, or structural integrity,prior to being subjected to the second nip. By regaining a level ofstructural integrity in the stem web, the deformation at the second nipprimarily occurs at the partially capped area of the stem and not at thestem itself. One way of measuring structural integrity is through theelastic modulus of the material. In the present invention, the coolingof the stem web increases the elastic modulus from the initial cappingstep to prevent deformation of the stem during the second nip.Preferably, the elastic modulus of the stem web is increased to a levelof at least 14 times greater than the elastic modulus of the stem web ata reference temperature essentially equal to the surface temperature atthe second nip. Another approach for measuring structural integrity isthrough the yield stress of the material. Similar to the elasticmodulus, yield stress increases as temperature decreases. In the presentinvention, it is preferred that the yield stress of the stem web at thecooling step increases to a level of at least 105 times that of theyield stress of the stem web at a reference temperature essentiallyequal to a surface temperature at the second nip.

In preparing the stem web for use with the present invention, thethickness of the backing 104 is conveniently between 4 mils (0.1 mm) and10 mils (0.25 mm), and depending on end use, stems 106 can be formed onthe backing in densities ranging from 100 to 3000 stems per square inch(15 to 465 stems/cm²). Stem diameters ranging from 0.005 to 0.020 inchesand stem heights ranging from 0.003 to 0.070 inches are consideredparticularly convenient, with the exact values dependent on the intendedend use. These stems are conveniently round cylinders, but square, oval,or other cross-sections are workable and desirable for specializedapplications.

The capping of the stem web is generally a time-temperature-pressurePhenomenon. Thus specific cap shapes or designs may be altered, oraffected, by selecting specific time, temperature, or pressureparameters at the nipping stage for a given process and selected stemweb materials. For example, U.S. Pat. No. 6,039,911, herein incorporatedby reference in its entirety, discloses a method and several devices forvarying the nip length and pressure. Additionally, it is generallyrecognized that the relative line speed of the surface of the nippingdevice and of the stem web impact the shape of the cap. Those skilled inthe art are capable of incorporating the cooling step of the presentinvention with conventional nipping processes and selected stem webmaterials to obtain a capped stem web with a desired cap size and shape.

In preferred embodiments, the forces between the first heated roll 110and the cooled roll 114, and the forces between the second heated niproll 128 and the cooled roll, are measured at both ends of each roll.The measurements are conveniently made with the use hydraulic actuatorswith embedded force and position measurements such as the PSC Cylindercommercially available from Miller Fluid Power of Bensenville, Ill. Itwill be known by those skilled in the art of such devices how toappropriately select these devices for the specific material, processconditions and equipment size being used.

Referring now to FIG. 3, a side view on a representative abrasivearticle 200, prepared according to the present invention is illustrated.The side of the capped stem web 140 bearing the stems can be called afirst major surface 202. The abrasive article 200 has then on a secondmajor surface 204 opposite the first major surface 202, the make coat206. At least partially embedded in the make coat 206 are abrasiveparticles 208. A size coat 210 is conveniently applied over the abrasiveparticles. The abrasive article 200 is conveniently prepared by makingthe capped stem web 140 as described above and then applying a make coat206 onto least a portion of the second major surface 204 of the backing104. Abrasive particles 208 are then at least partially embedded in themake coat 206, and the make coat is then at least partially cured. Asize coat 210 is applied over at least a portion of the at leastpartially cured make coat 206 and abrasive particles 208, and then thesize coat is cured. An optional supersize coat 212 may be applied overthe partially cured size coat 210.

Suitable materials for the make coat 206 include thermosetting organicpolymers. Examples of suitable thermosetting organic polymers includephenolic resins, urea-formaldehyde resins, melamine-formaldehyde resins,urethane resins, acrylate resins, polyester resins, aminoplast resinshaving pendant α,β-unsaturated carbonyl groups, epoxy resins, acrylatedurethane, acrylated epoxies, and combinations thereof. The make coat206, the abrasive article 200, or both may also include additives suchas fibers, lubricants, wetting agents, thixotropic materials,surfactants, pigments, dyes, antistatic agents (e.g., carbon black,vanadium oxide, graphite, etc.), coupling agents (e.g., silanes,titanates, zircoaluminates, etc.), plasticizers, suspending agents, andthe like. The amounts of these optional additives are selected toprovide the desired properties. The coupling agents can improve adhesionto the abrasive particles and/or filler. The binder chemistry may bethermally cured, radiation cured or combinations thereof. Additionaldetails on binder chemistry may be found in U.S. Pat. No. 4,588,419(Caul et al.), U.S. Pat. No. 4,751,137 (Tumey et al.), and U.S. Pat. No.5,436,063 (Follett et al.), the disclosures of which are incorporatedherein by reference in their entirety.

The abrasive articles 200 can contain 100% abrasive particles 208 orblends of such abrasive particles with other abrasive particles and/ordiluent particles. Examples of suitable conventional abrasive particlesinclude fused aluminum oxide (including white fused alumina,heat-treated aluminum oxide and brown aluminum oxide), silicon carbide,boron carbide, titanium carbide, diamond, cubic boron nitride, garnet,fused alumina-zirconia, and sol-gel-derived abrasive particles, and thelike. The sol-gel-derived abrasive particles may be seeded ornon-seeded. Likewise, the sol-gel-derived abrasive particles may berandomly shaped or have a shape associated with them, such as a rod or atriangle. Examples of sol gel abrasive particles include those describedU.S. Pat. Nos. 4,314,827 (Leitheiser et al.), U.S. Pat. No. 4,518,397(Leitheiser et al.), U.S. Pat. No. 4,623,364 (Cottringer et al.), U.S.Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.),U.S. Pat. No. 4,881,951 (Wood et al.), U.S. Pat. No. 5,011,508 (Wald etal.), U.S. Pat. No. 5,090,968 (Pellow), U.S. Pat. No. 5,139,978 (Wood),U.S. Pat. No. 5,201,916 (Berg et al.), U.S. Pat. No. 5,227,104 (Bauer),U.S. Pat. No. 5,366,523 (Rowenhorst et al.), U.S. Pat. No. 5,429,647(Larmie), U.S. Pat. No. 5,498,269 (Larmie), and U.S. Pat. 5,551,963(Larmie), the disclosures of which are incorporated herein by referencein their entirety. Additional details concerning sintered aluminaabrasive particles made by using alumina powders as a raw materialsource can also be found, for example, in U.S. Pat. Nos. 5,259,147(Falz), U.S. Pat. No. 5,593,467 (Monroe), and U.S. Pat. No. 5,665,127(Moltgen), the disclosures of which are incorporated herein by referencein their entirety. Additional details concerning fused abrasiveparticles, can be found, for example, in U.S. Pat. No. 1,161,620(Coulter), U.S. Pat. No. 1,192,709 (Tone), U.S. Pat. No. 1,247,337(Saunders et al.), U.S. Pat. No. 1,268,533 (Allen), and U.S. Pat. No.2,424,645 (Baumann et al.) U.S. Pat. No. 3,891,408 (Rowse et al.), U.S.Pat. No. 3,781,172 (Pett et al.), U.S. Pat. No. 3,893,826 (Quinan etal.), U.S. Pat. No. 4,126,429 (Watson), U.S. Pat. No. 4,457,767 (Poon etal.), U.S. Pat. No. 5,023,212 (Dubots et. al), U.S. (Gibson et al.), andU.S. Pat. No. 5,336,280 (Dubots et. al), and applications having U.S.Ser. Nos. 09,495,978, 09/496,422, 09/496,638, and 09/496,713, each filedon Feb. 2, 2000, and, 09/618,876, 09/618,879, 09/619,106, 09/619,191,09/619,192, 09/619,215, 09/619,289, 09/619,563, 09/619,729, 09/619,744,and 09/620,262, each filed on Jul. 19, 2000, and Ser. No. 09/772,730,filed Jan. 30, 2001, the disclosures of which are incorporated herein byreference in their entirety. In some instances, blends of abrasiveparticles may result in an abrasive article that exhibits improvedgrinding performance in comparison with abrasive articles comprising100% of either type of abrasive particle.

If there is a blend of abrasive particles, the abrasive particle typesforming the blend may be of the same size. Alternatively, the abrasiveparticle types may be of different particle sizes. Also, the abrasiveparticles may be uniformly distributed in the abrasive article orconcentrated in selected areas or portions of the abrasive article. Forexample, in a coated abrasive, there may be two layers of abrasiveparticles.

Examples of suitable diluent particles include marble, gypsum, flint,silica, iron oxide, aluminum silicate, glass (including glass bubblesand glass beads), alumina bubbles, alumina beads and diluentagglomerates. Abrasive particles according to the present invention canalso be combined in or with abrasive agglomerates. Abrasive agglomerateparticles typically comprise a plurality of abrasive particles, abinder, and optional additives. The binder may be organic or inorganic.Abrasive agglomerates may be randomly shape or have a predeterminedshape associated with them. The shape may be a block, cylinder, pyramid,coin, square, or the like. Abrasive agglomerate particles typically haveparticle sizes ranging from about 100 to about 5000 micrometers,typically about 250 to about 2500 micrometers. Additional detailsregarding abrasive agglomerate particles may be found, for example, inU.S. Pat. No. 4,311,489 (Kressner), U.S. Pat. No. 4,652,275 (Bloecher etal.), U.S. Pat. No. 4,799,939 (Bloecher et al.), U.S. Pat. No. 5,549,962(Holmes et al.), and U.S. Pat. No. 5,975,988 (Christianson), andapplications having U.S. Ser. Nos. 09/688,444 and 09/688,484, filed Oct.16, 2000, the disclosures of which are incorporated herein by referencein their entirety.

Grinding aids can be particularly useful in coated abrasive articles. Incoated abrasive articles, grinding aid is typically used in thesupersize coat 212, which is applied over the surface of the abrasiveparticles. Sometimes, however, the grinding aid is added to the sizecoat 210. Typically, the amount of grinding aid incorporated into coatedabrasive articles is about 50–300 g/m² (desirably, about 80–160 g/m²).

Grinding aids encompass a wide variety of different materials and can beinorganic or organic based. Examples of chemical groups of grinding aidsinclude waxes, organic halide compounds, halide salts and metals andtheir alloys. The organic halide compounds will typically break downduring abrading and release a halogen acid or a gaseous halide compound.Examples of such materials include chlorinated waxes liketetrachloronaphtalene, pentachloronaphthalene, and polyvinyl chloride.Examples of halide salts include sodium chloride, potassium cryolite,sodium cryolite, ammonium cryolite, potassium tetrafluoroboate, sodiumtetrafluoroborate, silicon fluorides, potassium chloride, and magnesiumchloride. Examples of metals include, tin, lead, bismuth, cobalt,antimony, cadmium, and iron titanium. Other miscellaneous grinding aidsinclude sulfur, organic sulfur compounds, graphite, and metallicsulfides. It is also within the scope of the present invention to use acombination of different grinding aids, and in some instances this mayproduce a synergistic effect. The preferred grinding aid is cryolite;the most preferred grinding aid is potassium tetrafluoroborate.

Further details regarding coated abrasive articles can be found, forexample, in U.S. Pat. No. 4,734,104 (Broberg), U.S. Pat. No. 4,737,163(Larkey), U.S. Pat. No. 5,203,884 (Buchanan et al.), U.S. Pat. No.5,152,917 (Pieper et al.), U.S. Pat. No. 5,378,251 (Culler et al.), U.S.Pat. No. 5,417,726 (Stout et al.), U.S. 5,436,063 (Follett et al.), U.S.Pat. No. 5,496,386 (Broberg et al.), U.S. Pat. No. 5,609,706 (Benedictet al.), U.S. Pat. No. 5,520,711 (Helmin), U.S. Pat. No. 5,954,844 (Lawet al.), U.S. Pat. No. 5,961,674 (Gagliardi et al.), and U.S. Pat. No.5,975,988 (Christinason), the disclosures of which are incorporatedherein by reference. Further details regarding bonded abrasive articlescan be found, for example, in U.S. Pat. No. 4,543,107 (Rue), U.S. Pat.No. 4,741,743 (Narayanan et al.), U.S. Pat. No. 4,800,685 (Haynes etal.), U.S. Pat. No. 4,898,597 (Hay et al.), U.S. Pat. No. 4,997,461(Markhoff-Matheny et al.), U.S. Pat. No. 5,038,453 (Narayanan et al.),U.S. Pat. No. 5,110,332 (Narayanan et al.), and U.S. Pat. No. 5,863,308(Qi et al.) the disclosures of which are incorporated herein byreference in their entirety.

From the above disclosure of the general principles of the presentinvention and the preceding detailed description, those skilled in thisart will readily comprehend the various modifications to which thepresent invention is susceptible. Therefore, the scope of the inventionshould be limited only by the following claims and equivalents thereof.

1. An apparatus for capping a stem web, said stem web having a backing and a plurality of stems extending from the backing, the apparatus comprising: a cooled roll; a first heated nip roll positioned to form a first nip wit the cooled roll; a second heated nip roll positioned to form a second nip with the cooled roll, wherein the cooled roll has a diameter that is at least 30% larger than a diameter of the first heated nip roll; sensors for measuring forces between the first heated nip roll and the cooled roll, and forces between the second heated nip roll and the cooled roll, at both ends of each roll, and actuators for adjusting positions of the rolls based on the output of the sensors.
 2. The apparatus according to claim 1, wherein the diameter of the cooled roll is at least 30% larger than a diameter of the second heated nip roll.
 3. An apparatus for capping a stem web, said stem web having a backing and a plurality of stems extending from the backing, the apparatus comprising: a cooled roll; a first heated nip roll positioned to farm a first nip with the cooled roll; a second heated nip roll positioned to form a second nip with the cooled roll, wherein the cooled roll has a diameter that is at least 30% larger than a diameter of the first heated nip roll.
 4. The apparatus of claim 3, further comprising sensors for measuring forces between the first heated nip roll and the cooled roll, and forces between the second heated nip roll and the cooled roll, at both ends of each roll.
 5. The apparatus of claim 3, further comprising actuators for adjusting positions of the rolls based on the output of the sensors.
 6. The apparatus of claim 3, wherein the diameter of the cooled roll is at least 30% larger than the diameter of the second heated nip roll. 